1. Field of the Invention
The present invention relates to a method and apparatus for analyzing a sample utilizing nuclear magnetic resonance and terahertz waves to obtain information about a material (sample). In particular, the present invention relates to a method and apparatus for analyzing a sample to obtain information about the three-dimensional structure of the molecule constituting a material, conformational alteration, relaxation, and the like and information about the terahertz-wave absorption or reflectance spectrum (typically, fingerprint spectrum) of the material.
2. Description of the Related Art
Methods of analysis utilizing electromagnetic-wave absorption provide significantly important information for the structural analysis of materials. For example, ultraviolet and visible absorption spectra have been used for characterization of excitation processes of electrons of materials. Near- and mid-infrared absorption spectra utilizing longer wavelengths play a significantly important role in structural and state analyses of organic and inorganic materials by excitation of chemical combination vibration of molecules to form spectra.
In contrast, until recently, terahertz waves (electromagnetic waves having a frequency in the range of several hundreds of gigahertz to several tens of terahertz) lying in the terahertz range, which is a further longer wavelength range, have not been used. However, in recent years, a high-performance light source for generating terahertz waves has been developed. Thus, terahertz waves have recently been receiving attention.
Like radio waves, terahertz waves can penetrate materials and thus provide internal information about materials. Furthermore, fingerprint spectra in the terahertz range provide structural information for identifying materials. That is, terahertz waves can be used for structural analysis that has been performed by the known infrared spectroscopy. The energy of terahertz waves is about two orders of magnitude lower than that of visible light. Thus, terahertz waves are suitably used to observe elementary excitation and relaxation of molecules, i.e., rotary motion of gas molecules, skeletal vibrations of molecules, intermolecular vibrations, and the like.
If peaks in fingerprint spectra lying in the terahertz range could be assigned and analyzed, information about elementary excitation and relaxation of molecules described above can be obtained, which is quite fascinating. In the infrared absorption spectra widely used now, peaks in spectra can be assigned with relatively high accuracy by calculating the combination vibration energy and the like of molecules using abundant spectrum databases, molecular orbital calculation, and the like. This is one reason for the wide use of infrared absorption spectra for molecular structure analysis, state analysis, and the like.
However, currently, peaks of materials in fingerprint spectra lying in the terahertz range are very difficult to assign. In the present circumstances, the number of spectrum data is small, assignments by means of molecular orbital calculation and the like have low accuracy, and the number of examples assigned is also small. This is attributed to the fact that absorption in the terahertz range varies in response to modes of motion of molecules. If peaks in fingerprint spectra lying in the terahertz range could be assigned and analyzed without any inhibition, the fingerprint spectra lying in the terahertz range should be widely used as a material-identifying tool.
From the background and present circumstances, it is desirable to develop an effective method for analyzing a fingerprint spectrum of a material in the terahertz range.
On the other hand, nuclear magnetic resonance (NMR) spectroscopy is a method of analysis of molecular structure and the like of organic materials. For example, when NMR spectra of hydrogen and carbon (to be exact, carbon-13 which is an isotope of carbon) constituting molecules of organic materials are measured, independent signals of all hydrogen and carbon are observed in response to chemical and magnetic environments thereof in the molecules. That is, hydrogen and carbon constituting the organic molecules can be distinguished at the molecular level. Furthermore, it is known that measurement of changes in the relaxation times of nuclear magnetic resonance signals (NMR signals) results in the evaluation of the interaction between materials and the evaluation of molecular mobility.
Japanese Patent Laid-Open No. 2005-156345 discloses a technique for measuring NMR signals of a protein by placing an aqueous solution of a protein sample in a static magnetic field and irradiating the sample with terahertz waves corresponding to a resonance frequency of unpaired spin present at the side chain of the protein sample. In this measurement, the application of a markedly strong magnetic field, for example, 21 T (tesla), to the aqueous solution sample of the protein sample results in Zeeman splitting of the unpaired spin present at the side chain of the protein, the Zeeman split levels being close to the energy of terahertz waves. The unpaired spin is excited by irradiation with terahertz waves corresponding to the resonance frequency of the unpaired spin, resulting in energy transfer via bonds such as hydrogen bonds around the unpaired spin. The change of bonds in the protein in the aqueous solution is observed from a change in the chemical shift of the NMR spectrum.
As described above, a combination of terahertz waves capable of exciting vibration and motion of the entirety of molecules and measurement of relaxation times of NMR signals for evaluation of large molecular mobility results in the assignment of peaks, which have been difficult to assign so far, in terahertz-wave fingerprint spectra. However, the assignment of the peaks in the fingerprint spectra is not reliable. Furthermore, a spectrometric technique for the assignment has not been established.
In the analysis described in Japanese Patent Laid-Open No. 2005-156345, it is essential that a measurement sample has unpaired spin. However, very limited organic materials have such unpaired spin. Thus, the method lacks versatility. Furthermore, in the method described above, the bonding state and the bonding distance in a very limited region around the unpaired spin are controlled and observed. That is, information about dynamic behavior, such as molecular vibration and molecular mobility, is not obtained.